Method of radiusing the edge of an aperture electrolytically



May 21, 1968 J. TAYLOR 3,

METHOD OF RADIUSING THE EDGE OF AN APERTURE ELEC'IROLY'IICALLY FiledJuly 21, 1965 2 Sheets-Sheet 1 liiv Inventor Attorneys May 21, 1968 .1.TAYLOR 3,384,563

METHOD OF RADIUSING THE EDGE OF AN APERTURE ELECTROLYTICALLY Filed July21, 1965 2 Sheets-Sheet 2 3,384,563 METl-IUD OF RADIUSENG THE EDGE OF ANAPERTURE ELECTROLYTICALLY John Taylor, Derby, England, assiguor toRolls-Royce Limited, Derby, Derbyshire, England, a British company Filed.luly 21, 1965, Ser. No. 473,634 Claims priority, application GreatBritain, Aug. 27, 1964, 35,239/ 64 6 Claims. (Cl. 204143) This inventionconcerns electrolytic machining and in particular a method of smoothingthe sharp edge(s) of an aperture within a metal workpiece.

The invention is particularly applicable to the smoothing or radiusingof the sharp edge(s) which are left after machining lade roots onturbine or compressor rotor discs for gas turbine engines. If theseedges are left sharp on such components they are liable to initiatecracks and thus cause breakdown of the engine. It has previously beenproposed to radius these edges by means of an abrasive string usedmanually but such a method is expensive, time consuming and notparticularly satisfactory.

According therefore to the present invention there is provided a methodof smoothing the sharp edge(s) of an aperture within a metal workpiececomprising providing a nozzle-electrode assembly, the nozzle of which isthe same shape as, but of somewhat larger internal dimensions than, saidaperture, disposing said assembly adjacent said aperture, causingelectrolyte to How continuously through said nozzle-electrode assemblyand into said aperture such that it passes over the sharp edge(s) ofsaid aperture, and making said workpiece electrically positive relativeto said assembly whereby the sharp edge(s) of said aperture is or areremoved by electrolytic action.

Thus it is possible to smooth or radius the sharp edges which are leftafter machining the blade roots on turbine or compressor rotor discselectrolytically and it has been found that this method is most suitablefor this application.

Preferably the nozzle-electrode assembly comprises an outer tubularstructure of electrically non-conductive material within which there isdisposed an electrically conductive rod or plate which is madeelectrically negative with respect to said workpiece.

In a preferred method the electrolyte is caused to flow continuouslywhilst the workpiece and electrode are electrically biased relative toone another. This is most important if accurate results are to beobtained since, should the electrolyte fiow stagnate deep etching mayoccur at the points of stagnation and a smooth edge will not beobtained.

Preferred electrolytes are those containing sodium ions and thussolutions of sodium chloride, sodium sulphate or sodium nitrate may beused.

The invention is illustrated merely by way of example in theaccompanying drawings, in which:

FIGURE 1 is a general view of apparatus which may be used in employingthe method according to the present invention,

FIGURE 2 is a detailed side elevation of part of the apparatus shown inFIGURE 1,

FIGURE 3 is a sectional view on line 3-3 of FIG- URE 2,

FIGURE 4 is a sectional View on line 44 of FIG- URE 3, and

FIGURE 5 is a view similar to FIGURE 3 of an alternative form ofnozzle-electrode assembly used in machining a gas turbine engine turbinerotor disc.

Referring to the drawings and particularly to FIG- URES 1 to 4 thereofthere is shown a tank containing electrolyte 11. A work table 12 isdisposed within "ice tank 10 and clamped thereon is an annular metalworkpiece 13 having formed therein eight circular holes 14 having sharpedges which it is desired to smooth or radius.

Slidably mounted on the table 12 is a support 15 having a clamp 16 fixedthereto. Clamp 16 rigidly holds a tube 17 therein, the tube 17communicating with and being fixed to an annular manifold 18. Projectingfrom and communicating with annular manifold 18 are eight tubularextensions 19 to the lower ends of which are attached electricallynon-conductive tubular nozzles 20. Fixed within and connected to thetubular extensions 19 are metal electrodes 21. Set screws 22 threadedwithin apertures in the tubular extensions 19 make electrical contactwith the electrodes 21. The electrically non-conductive nozzles 20,together with the metal electrodes 21, constitute nozzle-electrodeassemblies.

As seen in FIGURES 1 and 2 the upper end of tube 17 has fixed thereto aflexible pipe which communicates with the outlet side of a pump 31. Theinlet side of pump 31 communicates by a further flexible pipe 32 withthe outlet from tank 10 from which it receives electrolyte. Pump 31 isdriven by an electric motor 34 and, when in operation, pumps electrolytecontinuously from the tank 10 through tube 17 and thus through tubularnozzles 20. Electrolyte which has flowed through nozzles 20 passes overtable 12 and into the electrolyte 11 within tank 10 to be used again byrecirculation.

To radius the sharp edges of holes 14, the nozzleelectrode assembliesconstituted by tubular nozzles 20 and electrodes 21 are disposed closelyadjacent the upper ends of holes 14, as clearly seen in the figures. Itwill be noted, particularly from FIGURES 3 and 4, that the internaldimension of each tubular nozzle 20 is somewhat larger than that of thehole 14 which it is desired to machine and it will also be noted thatthe shape of each tubular nozzle 20 is identical with that of each hole14. The pump 31 is actuated by electric motor 34 and a continuous flowof electrolyte therefore fiows through tubular nozzles 20 and intoapertures 14, the electrolyte being forced over the sharp edges of holes14 due to the relative sizes and shapes of tubular nozzles 20 and holes14. The workpiece 13 is made electrically positive with respect toelectrodes 21, the electrodes 21 being made electrically negative byconnecting electrical leads to the set screws 22. Electrolytic actiontakes place and the sharp edges of the apertures 14 over which theelectrolyte flows are machined away by this electrolytic action, thesharp edges thereby being smoothed or radiused.

The method is particularly suitable for use in machining apertureswithin turbine rotor and compressor rotor discs of gas turbine enginesand a modified electrode for use in such an arrangement is shown inFIGURE 5. In FIG- URE 5 there is shown a turbine disc which has beenmachined to provide a fir tree blade root 41 having an enlarged radiallyinner end 42. The aperture formed at the radially inner end 42 has sharpcorners as a result of the machining process and these are liable toinitiate cracks if left sharp. A generally elliptical tubularnozzleelectrode assembly 43 is provided as shown in FIGURE 5, the nozzlebeing of the same shape as but somewhat larger than the aperture formedat the radially inner end 42. As in the embodiment of FIGURES l to 4,the nozzle-electrode assembly comprises an electrically non-conductiveouter tubular portion 44 and an inner electrode 45 which is madeelectrically negative with respect to the turbine rotor disc 40. Thesharp edges of the aperture at the radially inner end 42 are now removedby electrolytic action in the manner described above with reference toFIGURES 1 to 4.

It will be appreciated that the arrangement described above may beemployed in any location in which it is present invention it isimperative that the electrolyte fiow should not be allowed to stagnatesince if this happens deep etching is liable to take place at the pointof stagnation and the smoothing or radiusing operation is therebyhindered.

I claim: I

1. A method of smoothing the sharp edge of an aperture within a metalworkpiece comprising providing a nozzle-electrode assembly, the nozzleof which is the same shape as, but of somewhat larger internaldimensions than, said aperture, disposing said assembly adjacent saidaperture, causing electrolyte to flow continuously through saidnozzle-electrode assembly and into said aperture such that it passesover the sharp edge of said aperture, and making'said workpieceelectrically positive relative to said electrode whereby the sharp edgeof said aperture is removed by electrolytic action.

2. A method of smoothing the sharp edge of an aperture within a metalworkpiece comprising providing a nozzle-electrode assembly comprising anouter tubular nozzle structure of electrically non-conductive materialand an electrically conductive electrode member disposed within saidouter tubular nozzle structure, said nozzle being the same shape as, butof somewhat larger internal dimensions than, said aperture, disposingsaid assembly adjacent said aperture, causing electrolyte to flowcontinuously through said nozzle and into said aperture such that itpasses over the sharp, edge of said aperture, and making said workpieceelectrically positive relative to said electrode whereby the sharp edgeof said aperture is removed by electrolytic action.

3. A method of smoothing the sharp edge of an aperture within a metalworkpiece comprising providing a nozzle-electrode assembly, the nozzleof which is the same shape as, but of somewhat larger internaldimensions than, said aperture, disposing said assembly adjacent saidaperture, causing electrolyte to flow continuously through saidnozzle-electrode assembly and into said aperture such that it passesover the sharp edge of said aperture, and making said workpieceelectrically positive relative to said electrode whereby the sharp edgeof said aperture is removed by electrolytic action, said electrolyteflowing continuous ly whilst the workpiece and nozzle-electrode assemblyare electrically biased relative to one another.

4. A method of smoothing the sharp edge of an aperture within a metalworkpiece comprising providing a nozzle-electrode assembly, the nozzleof which is the same shape as, but of somewhat larger internaldimensions than, said aperture, disposing said assembly adjacent saidaperture, causing electrolyte containing sodium ions to flowcontinuously through said nozzle-electrode assembly and into saidaperture such that it passes overthe sharp edge of said aperture, andmaking said workpiece electrically positive relative to said electrodewhereby the sharp edge of said aperture is removed by electrolyticaction.

5. A method of smoothing the sharp edge of an aperture within. a metalworkpiece comprising providing a nozzle-electrode assembly, the nozzleof which is the same shape as,'but of somewhat larger internaldimensions than, said aperture, disposing said assembly adjacent saidaperture, selecting electrolyte from the class including sodiumchloride, sodium sulphate and sodium nitrate solutions, causing theelectrolyte to flow continuously through said nozzle-electrode assemblyand into said aperture such that it passes over the sharp edge of saidaperture, and making said workpiece electrically positive relative tosaid electrode whereby the sharp edge of said aperture is removed byelectrolytic action.

6. A method of smoothing the sharp edge of an aperture within a gasturbine rotor disc comprising providing a nozzle-electrode assembly, thenozzle of which is the same shape as, but of somewhat larger internaldimensions than, said aperture, disposing said assembly adjacent saidaperture, causing electrolyte to flow continuously through saidnozzle-electrode assembly and into said aperture such that it passesover the sharp edge of said aperture, and making said workpieceelectrically positive relative to said electrode whereby the sharp edgeof said aperture is removed by electrolytic action.

References Cited UNITED STATES PATENTS 3,309,294 3/1967 Goodwin 204l43FOREIGN PATENTS 703,838 2/1954 Great Britain.

ROBERT K. MIHALEK, Primary Examiner.

1. A METHOD OF SMOOTHING THE SHARP EDGE OF AN APERTURE WITHIN A METALWORKPIECE COMPRISING PROVING A NOZZLE-ELECTRODE ASSEMBLY, THE NOZZLE OFWHICH IS THE SAME SHAPE AS, BUT OF SOMEWHAT LARGER INTERNAL DIMENSIONSTHAN, SAID APERTURE, DISPOSING SAID ASSEMBLY ADJACENT SAID APERTURE,CAUSING ELECTROLYTE TO FLOW CONTINUOUS-